The New Zealand heavyweight tested positive as part of a anti-doping examination conducted the very day of his 11th-round stoppage versus UK boxer Fabio Wardley.
The British boxer along with Joseph Parker engaged in a pulsating bout held in London last October to establish the next WBO mandatory challenger against undisputed world heavyweight champion Oleksandr Usyk.
Joseph Parker had been the leading contender to challenge the champion following stringing together an impressive six wins in a row, however placed his mandatory challenger status at stake in the UK and suffered a stoppage in round eleven.
A routine test given to Joseph Parker via the Voluntary Anti-Doping Agency the day of the match returned positive and leaves the veteran boxer in a difficult position to prove his innocence.
His promotion team released a statement declaring: "Vada alerted all relevant parties about Parker tested positive after a doping test administered on the 25th October. While the matter is investigated, no further statements are planned at this time."
Joseph Parker became heavyweight champion six years ago until he surrendered his WBO belt through a points decision to British star Joshua at the Millennium Stadium in 2018.
Parker became a frequent visitor on British soil after that, having eight matches in total on UK territory and transferring to the Irish capital for training camps under highly regarded trainer Andy Lee in recent years.
Under the tutelage of Lee, Parker recovered from the 2022 setback versus Joe Joyce to secure a string of victories positioning him front of the queue to meet Oleksandr Usyk until he suffered defeat to Wardley.
Following Parker returned a positive test when he fought Wardley, allegedly for cocaine, an inquiry regarding the results has commenced.
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